Device for eliminating low frequency radiation of monitor

ABSTRACT

A device for eliminating low frequency radiation of a computer monitor is disclosed, including a pair of first conductive plates disposed on two opposite sides of a cathode ray tube of the monitor to generate a radiation signal thereon that is induced by the low frequency radiation of the monitor, the radiation signal being applied to a circuit which amplifies and inverts the radiation signal to generate an in inverted and amplified output signal, the output signal being applied to a pair of second conductive plates arranged on another two opposite sides of the cathode ray tube to cancel the low frequency radiation of the cathode ray tube.

FIELD OF THE INVENTION

The present invention relates generally to computer monitor and inparticular to a device for eliminating the low frequency radiationemitting from an operating computer monitor.

BACKGROUND OF THE INVENTION

Computer systems have been widely used nowadays. Monitors for displayingthe operation and status of the computer systems usually comprise acathode ray tube which emits an electron beam to a screen and shows animage thereon. The operation of the cathode ray tube gives offelectromagnetic radiation, especially low frequency radiation, which maycause physical damage to the computer operators for a long termoperation of the monitor.

Most of the developed countries have regulations to limit theelectromagnetic radiation emitted from an operating monitor, such as TCO(The Swedish Confederation of Professional Employees) regulation. Inaccordance with the TCO regulation, the low frequency radiation of acomputer monitor is measured by placing a detector 10 at a distance of30 cm away from the front surface or screen 12 of the monitor 11 (seeFIG. 1 of the attached drawings) and the measured radiation should belimited within 1 V/m.

One of the conventionally ways to reduce the low frequency radiation ofthe computer monitor is to use a cathode ray tube with lower surfaceimpedance and to ground the surface of the cathode ray tube. Such amethod, however, needs to generate negative pulses from a high voltagetransformer to cancel the surrounding magnetic field. This iscomplicated and expensive.

Further, the low frequency radiation emitted from the cathode ray tubeincludes a vertical frequency of 50-100 Hz and a horizontal frequency of24-80 Khz. Such a conventional way is only capable to reduce or suppressthe horizontal frequency and can not solve the low frequency radiationproblem of the computer monitor completely.

Another conventional way to handle such a low frequency radiationproblem is to provide a coating on the monitor screen which is capableto resist or block the low frequency radiation. The application of thecoating, however, is difficult for such a coating usually containsenvironmental pollution material or toxicant material.

Thus it is desirable to provide a device to overcome or eliminate thelow frequency radiation problem encountered in the computer monitor art.

SUMMARY OF THE INVENTION

The principal object of the present invention is to provide a device toeliminate the low frequency radiation generated by an operating computermonitor which does not include a low surface impedance cathode ray tubeor does not made use of any environmental pollution material coating onthe monitor screen.

Another object of the present invention is to provide a device which iscapable of substantially completely eliminating the low frequencyradiation generated in an operating monitor.

A further object of the present invention is to provide a device foreliminating the low frequency radiation of a monitor which is completelyenclosed inside the monitor casing so as not to affect to any extent theoutside configuration of the monitor.

In accordance with the present invention, there is provided a device foreliminating low frequency radiation of a computer monitor, comprising apair of first conductive plates disposed on two opposite sides of acathode ray tube of the monitor to generate a radiation signal thereonthat is induced by the low frequency radiation of the monitor, theradiation signal being applied to a circuit which amplifies and invertsthe radiation signal to generate an inverted and amplified outputsignal, the output signal being applied to a pair of second conductiveplates arranged on another two opposite sides of the cathode ray tube tocancel the low frequency radiation of the cathode ray tube.

In accordance with an aspect of the present invention, the firstconductive plates are disposed on side edge portions of the monitorscreen and the second conductive plates are arranged on different sideedge portions of the monitor screen.

In accordance with another aspect of the present invention, the firstconductive plates are disposed on side edge portions of the monitorscreen while the second conductive plates are arranged on top and bottomsides of the cathode ray tube.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood from the followingdescription of preferred embodiments thereof, with reference to theattached drawings, wherein:

FIG. 1 is a schematic view showing a test arrangement in accordance withthe TCO regulation;

FIG. 2 is a schematic view showing a low frequency radiation eliminatingdevice in accordance with a first embodiment of the present invention,mounted on a cathode ray tube of a computer monitor;

FIG. 3 is a schematic view showing a low frequency radiation eliminatingdevice in accordance with a second embodiment of the present invention;

FIG. 4 is a circuit diagram in accordance with the present invention;

FIG. 5 is another circuit diagram in accordance with the presentinvention;

FIG. 6 is a plot demonstrating the radiation signal of 31.5 KHzgenerated in an operating computer monitor;

FIG. 7 is a plot showing the output signal of the radiation eliminatingdevice of the present invention in response to the radiation of 31.5 KHzshown in FIG. 6;

FIG. 8 is a plot demonstrating the radiation signal of 64 KHz generatedin an operating computer monitor; and

FIG. 9 is a plot showing the output signal of the radiation eliminatingdevice of the present invention in response to the radiation of 64 KHzshown in FIG. 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to the drawings and in particular to FIG. 2, which showsa schematic front view of a computer monitor with a low frequencyradiation eliminating device constructed in accordance with a firstembodiment of the present invention mounted thereon, the low frequencyradiation eliminating device of the present invention comprises a pairof first conductive plates 22, preferably made of copper- or iron-basedalloys, disposed on two opposite side edge portions of the screen of thecathode ray tube designated at 21. The first plates 22 are to receivethe radiation generated during the operation of the computer monitor andin response thereto to generate a signal induced on the first plates 22to be applied to a circuit to be described later. The circuit receivesthe signal and then inverts and amplifies the signal. The inverted andamplified signal is then applied to a pair of second conductive plates23, preferably made of a copper- or iron-based alloy, disposed on theother two opposite side edge portions of the screen of the cathode raytube 21 to cancel the radiation generated by the cathode ray tube 21.

In accordance with the present invention, preferably the first plates 22have a size larger than the second plates 23.

Alternatively, the second plates 23 may be arranged on the top andbottom sides of the cathode ray tube 21, as shown in FIG. 3.

In both cases, the first plates 22 and the second plates 23 are disposedinside a monitor casing (not shown) that encloses the cathode ray tube21 so that the overall outside configuration of the monitor is notaltered.

With reference to FIG. 4, wherein a circuit for inverting and amplifyingthe radiation signal induced on the first plates 22 is shown, thecircuit comprises an inverting amplifier circuit constituted by atransistor Q1. The radiation signal (of the frequency 64 KHz or 31.5KHz) induced on the first plates 22 is applied to an input of thecircuit and the radiation signal that is applied to the circuit is firstsent through a variable resistor (VR) to adjust the amplitude thereofwhich determines the amplification ratio of the transistor Q1. Theemitter of the transistor Q1 constitutes an output terminal of thecircuit so that the transistor Q1 amplifies and inverts the input signalfrom the variable resistor VR and outputs a negative (or inverted)amplified signal relative to the radiation signal from the first plates22.

The negative output of the circuit is then transmitted to the secondplates 23 to cancel the radiation generated by the cathode ray tube 21.

Alternatively, as shown in FIG. 5, the circuit may be a high inputimpedance inverting amplification circuit comprising a buffer 24 and anamplification circuit 25. The buffer 24 is composed of a transistor Q2which stabilizes the radiation signal received from the first plates 22and applies the signal to the amplification circuit 25 which thenamplifies and inverts the signal. The amplification circuit 25 iscomposed of transistors Q3 and Q4. The transistor Q3 serves to invertthe signal from the transistor Q2, while the transistor Q4 amplifies theinverted signal. The output signal of the transistor Q4 is an invertedand amplified signal of the radiation signal from the first plates 22and is applied to the second plates 23 to cancel the radiation generatedby the cathode ray tube 21.

It is quite apparent that besides the exemplary circuits illustrated inFIGS. 4 and 5, there are many other circuit arrangements which arecapable to achieve the same function of amplification and inversion ofthe radiation signal from the first plates 22 and modifications made onthe circuits should be considered within the scope covered by thepresent invention.

FIG. 6 shows the radiation signal of 31.5 KHz that is generated by thecathode ray tube 21 and induced on the first plates 22. The radiationsignal is then amplified and inverted by the circuit of either FIG. 4 orFIG. 5 and then applied to the second plates 23. The inverted andamplified output signal of the circuit is shown in FIG. 7. As is quiteapparent by comparing FIGS. 6 and 7, the radiation signal generated bythe cathode ray tube 21 can be almost completely canceled or eliminatedby the output signal from the circuit. FIG. 8 shows the radiation signalof the frequency of 64 KHz which after being applied to the circuit ofeither FIG. 4 or FIG. 5 to be inverted and amplified thereby generatesan output signal illustrated in FIG. 9. Obviously, the cathode ray tuberadiation of 64 KHz may also be almost eliminated by the output signalfrom the circuit.

Thus, the present invention provides a device to effectively eliminatethe low frequency radiation generated by a cathode ray tube withoutusing any low surface impedance cathode ray tube or without treating thecathode ray tube screen with any coating.

Although preferred embodiments are described to illustrate the presentinvention, it is understood that the present invention is not limited tothe specific examples illustrated herein and in the drawings and is onlydefined by the appended claims as follows.

What is claimed is:
 1. A device for eliminating low frequency radiationof a computer monitor wherein the monitor includes a cathode ray tubewith a screen having edge portions,the device comprising a pair of firstconductive plates disposed on two opposite first ones of the side edgeportions of the screen of the cathode ray tube of the monitor togenerate a radiation signal on the pair of first plates that is inducedby the low frequency radiation of the monitor, a circuit which amplifiesand inverts the induced radiation signal to generate an inverted andamplified output signal, a pair of second conductive plates arranged onanother two opposite second ones of the side edge portions of the screenof the cathode ray tube and the second plates are connected with thecircuit to cancel the low frequency radiation of the cathode ray tube.2. The device as claimed in claim 1, wherein the conductive platescomprises metal plates made of a metal selected from the groupconsisting of copper-based alloys and iron-based alloys.
 3. The deviceas claimed in claim 1, wherein the circuit comprises an invertingamplifier.
 4. The device as claimed in claim 1, wherein the secondplates are smaller in size than the first plates.
 5. The device asclaimed in claim 1, wherein the first conductive plates are disposed onlateral side edge portions of a screen of the cathode ray tube and thesecond conductive plates are disposed on top and bottom sides of thecathode ray tube.